Because of superior processing ability, rigidity, electrical property, etc., styrene-based resins are widely used in various industrial fields for office equipments such as personal computers, word processors, printers and copying machines, household appliances such as TVs, VTRs and stereos, electric and electronic equipments, automobile products and other miscellaneous goods. Particularly, the flame retardant styrene-based resin is mainly used for TV housings.
In spite of superior processing ability and physical properties, use of styrene-based resins was accompanied with safety problem because they burn easily. Thus, researches were performed consistently to offer flame retardance to styrene-based resins. Various halogen-based flame retardants, phosphorus-based flame retardants and inorganic flame retardants are added to attain the flame retardance. Up to now, halogen-based flame retardants are used the most widely since they offer superior flame retardance.
Styrene-based resins have been used in many applications because of superior processing ability. With the recent trend of enlargement of household appliances and office equipments and for cost reduction, need of processing of styrene-based resins into thin film is growing. However, conventional flame retardant styrene-based resins are poor in impact resistance and rigidity to satisfy such need. In addition, superior fluidity is needed for the resins for extrusion and processing with better productivity.
The most general method of improving impact resistance of flame retardant styrene-based resins is adding an impact modifier. Currently, a styrene-butadiene block copolymer is used the most widely. Japanese Patent Laid-Open No. 1999-29687 disclosed a method of improving flame retardance and impact strength by adding an ethylene-methyl methacrylate copolymer to a resin. However, there is no mention of comparison with other impact modifiers.
Japanese Patent Laid-Open No. 1999-343373 disclosed a method of improving impact resistance of an impact-resistant polystyrene resin by controlling particle size distribution of the rubber particles of the resin. This method is advantageous in that a polystyrene resin having large rubber particles can be used along with a polystyrene resin having small rubber particles to offer superior impact resistance even after flame retardance treatment. Japanese Patent Laid-Open No. 1994-256618 disclosed a method of adding polyphenylene ether to improve Izod impact strength and falling weight impact strength of a flame retardant resin.
While the conventional methods could attain improvement of Izod impact strength and falling weight impact strength of a flame retardant styrene-based resin to some degree, the problem of reduction of rigidity and fluidity was not solved. Particularly, when an impact modifier is used to process large and complex products, such appearance problems as flow mark tend to occur frequently.
Thus, a flame retardant styrene-based resin with high impact strength capable of improving appearance problem while maintaining good fluidity and rigidity is urgently needed.